When joining heavy steel, it is advantageous to perform the arc welding process from a single side with the plates generally horizontal so the electrode used to deposit metal can move along the flat heavy plates at the joint between the edges of the plate to perform the joining operation. This type of plate welding is used for making large oil rigs which require large segments of steel plates to be joined together for constructing the pontoon area of the oil rigs. It is also used in shipbuilding for ship hulls and deck plate.
The present invention is directed to a single side type of welding operation for joining two heavy steel plates having their edges butted together. These plates have a tapered edge to define a channel. Below this channel is a copper backing strip with a recess machined into it to accommodate the addition of a backup flux. This recessed cavity is filled with a granular flux to help form the back side of the weld bead as the root pass or first layer of molten metal is applied along the bottom portion of the channel between the edges of the heavy steel plates. Other mediums, such as fiber tape and ceramic tile, may also be used to form the backside of the weld bead.
In the past, there was substantial difficulty in making the root pass such that the metal would not blow through into the flux compromising the root pass integrity and consistency. When a single electrode was used to deposit the root pass between the heavy steel plates, the heat generated in the lower area of the channel between the plates caused a burn through. Consequently, the punch through problem was solved by The Lincoln Electric Company in its modified series arc process wherein two adjacent electrodes were employed for the root pass arc welding process, as shown in Shutt U.S. Pat. No. 4,246,463. This allowed a softer arc welding approach wherein the first electrode primarily deposited the molten metal between the edges of the plate and melted the plates, while the electrode followed behind the first electrode spreads out the molten metal to form an acceptable bead profile in the root pass. In some instances, even a third trailing electrode was used so that the necessary metal was deposited for the root pass without requiring the high heat energy adjacent any one of the electrodes. This process was used successfully; however, it is extremely complex. The use of a simple process for creating the root pass between the edges of heavy steel plates which was reproducible and did not cause cracking or overheating was desired but not available.